# Wetted Perimeter

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Wetting perimeter is the portion of the channel that is in contact with the fluid flowing.

## Wetted perimeter formulas

 $$\large{ P_w = \frac{ A_c }{ r_h } }$$ $$\large{ P_w = 2 \; h \; \sqrt {1 + z^2 } }$$ (hydraulic radius) $$\large{ P_w = r \; \theta }$$ (Hydraulic Radius of a Partially Full Pipe (Less than Half Full)) $$\large{ P_w = 2 \; \pi \; r - r \; \theta }$$ (Hydraulic Radius of a Partially Full Pipe (More than Half Full))

### Where:

$$\large{ P_w }$$ = wetting perimeter

$$\large{ A_c }$$ = area cross-section of flow

$$\large{ \theta }$$   (Greek symbol theta) = degree

$$\large{ h }$$ = depth of fluid

$$\large{ r_h }$$ = hydraulic radius

$$\large{ \pi }$$ = Pi

$$\large{ r }$$ = radius

$$\large{ z }$$ = width of channel slope